The present invention relates to an oscillating circuit arrangement that is adapted for a component module, and specifically to the kind of oscillating circuit arrangements that are adapted to produce signals with a high frequency and small frequency span, such as frequencies and/or bit rates within, at least, the MHz or Mbit/s range and above.
Oscillating circuit arrangements of this kind normally comprise an amplifying circuit and the circuit that generates the oscillating signal, usually in the form of an oscillating element, and more specifically an oscillating element with a pronounced resonance frequency, a so-called resonance element or component, with electric wiring and compensating networks or elements, such as inductance elements, as needed.
An oscillating circuit of this kind can preferably be useful as a separate circuit arrangement to be able to generate a synchronizing signal in circuit internal signal processing to one or several signal processing units. It can also be used to generate clock pulses within a communication system, to transmit information carrying signals where the pulses together with data signals can be transmitted from a signal transmitting unit onto a transmission line or in a signal receiving unit.
The invention is based on the principle that in each case the oscillating circuit arrangement is to be supported by a carrier substrate forming a component module where the top layer of the carrier substrate upholds the discrete components of the oscillating circuit arrangement and an integrated circuit arrangement.
Oscillating circuit arrangements of the kind that generate a signal with a chosen high frequency of at least 100 MHz or more and with a small frequency span are earlier known in several different embodiments with regards to chosen components such as oscillating element, chosen circuit arrangement and mechanical disposition. Such an oscillating circuit arrangement can be a part of a phase-locked loop (PLL) system where the oscillating component or element consists of a voltage-controlled oscillator (VCO). Oscillating circuit arrangements where the oscillating component consists of a surface acoustic wave (SAW) component are designated as VCSOs (voltage-controlled SAW oscillators) or VCSO systems.
U.S. Pat. No. 4,760,352 and No. 4,325,032 show and describe examples of oscillating circuits with SAW-elements or -components. Other units are shown and described in European patent publication Nos. EP 0 527 468; EP 0 495 316; EP 0 217 713; and EP 0 241 236; Japanese patent publication No. JP-A- 2 207 601; and U.S. Pat. No. 5,029,267.
An additional oscillating circuit arrangement of this kind, where the complete system or parts of the system can be integrated on one or several receiver circuits, is known as a frequency-controlled SAW oscillator (FCSO) or FCSO system.
Oscillating circuit arrangements can be used in both earlier mentioned VCSO- and FCSO-systems where a SAW-component is used and where the circuit arrangement is based upon a feedback of the frequency of the SAW-component at the resonance frequency of the filter.
Crystal controlled SAW oscillators have also been described, where the crystal, used as an oscillating element, is mounted in its own oscillating unit, adapted to generate the necessary reference frequency to the SAW-component and its oscillator circuit.
Arrangements of this kind are based upon the fact that, at resonance, the SAW-filter component presents a phase shift of 90.degree. between the input and output terminals. The phase-shifted output signal is fed back through an amplifier that is phase-angle adjustable around the resonance frequency at a range of 60.degree. to 120.degree.. The phase variations and the amplifier can easily be operated by a control voltage with these kind of oscillating circuit arrangements. One can thus achieve an accurate frequency and frequency tuning around the resonance frequency of the SAW-filter with the aid of such a control voltage.
A SAW-component is characterized by a very narrow frequency span, with typically a few-percent deviation, depending on the chosen type of SAW-component, and a very pure frequency with well repressed subharmonics and harmonics. SAW-components have proven suitable for very high oscillating frequencies, frequencies from some tens of MHz to a number of GHz.
Current experience with known voltage-controlled SAW-components used as VCOs and VCSO-oscillators is that these components are, in terms of spatial volume, very large compared to the component modules and/or standard integrated circuits typically used. The function of such an oscillating circuit arrangement requires that the SAW-component, usually together with compensating networks, such as inductance elements, electric wiring and amplifiers as needed, is covered in some kind of casing, such as a ceramic holder with a metal cup, and is thus very expensive, particularly since this casing, because of the sensitivity of the SAW-component, often has to be evacuated and airtight. This technique, and the space that is thereby needed, has resulted in that oscillating circuit arrangements of this kind have only been brought to use in more exclusive circumstances where the various functional requirements are so high, or where the number of units is so low, that the cost is of secondary importance.
For all the above-mentioned oscillating circuit arrangements, one can say that the mechanical disposition of such an oscillating circuit arrangement indicates that the oscillating component, necessary compensating networks, such as inductance elements, electric wiring, amplifiers and so on, is coordinated in a separate evacuated airtight metal or ceramic unit with a metal casing. Such a unit is physically separated and side-oriented from the component module pertaining to other functions such as those used in telecommunication and associated selectors or other equipment. Oscillating circuit arrangements of this kind mounted in such a unit, cover a surface of at least 20.times.20 mm if not more.
The basic principles of the present invention do not directly depend on the chosen resonance element, but in the following, a SAW-element or SAW-component will exemplify one of several available, and at present most suitable, resonance elements. It will be understood that surface transverse wave (STW) components and surface skimming bulk wave (SSBW) components are intended to be included in the expression "SAW-component".
To further clarify the earlier oscillating circuit arrangements with frequency accuracy, a category called crystal-oscillators, using crystals as oscillating- or resonance-elements, can be mentioned. A crystal oscillator of this kind works in the range of some hundreds of MHz in its keynote, or fundamental frequency, and up to a few hundreds of MHz if one of the harmonics of the crystal is used. Oscillating circuit arrangements with a crystal as a resonance element are used as oscillators and voltage-controlled crystal oscillators (VCXOs). Such oscillators are available as small hole mounted plastic caps and as very small surface mounted multilayer ceramic (MLC) modules. Oscillating circuit arrangements of this kind are, cost-wise, relatively inexpensive, but they have more frequency- and phase-noise (in other words, stronger subharmonics and harmonics) than the SAW-component arrangements and can therefore not produce a frequency with the same purity as the one produced by a SAW-component.
Oscillating circuit arrangements used to generate signals with frequencies in the range of some hundreds of MHz to some GHz use quarter-wave resonators. These are based upon a resonator comprising a conductor, made out of a specific material, with a length that corresponds to a quarter of the wavelength of the resonance frequency.
Oscillating circuit arrangements of the type DCSO (digital control SAW oscillator) use an oscillator controlled by a digital signal. The oscillator is generally a VCSO where the control voltage is generated by a digital-to-analog (D/A) converter. By supplying a digital command to the DCSO, one can get the desired controlled voltage out of the D/A-converter. The D/A-converter can either give an output voltage as a function of input data or it can be a potentiometer controlled by a digital signal to achieve the desired control voltage. A D/A converter or digital trim potentiometer can receive its information in either parallel or serial form. They can obviously be equipped with some kind of memory so that the oscillator can be restarted at a predetermined frequency after, for instance, a power failure.
Considering the known systems described above, it should be regarded as a technical problem to create the conditions where a separately cased oscillating unit is not required and to put components belonging to an oscillator on a component module meant for other functions controlled by the oscillator circuit.
A technical problem resides in being able to see the consequences and importance of limiting the size and number used of discrete cased components, applied to the carrier substrate of the component module.
It is a technical problem to be able to create the circumstances needed to apply discrete components to a carrier substrate and, for such components that normally require airtight casing, to create circumstances so that an airtight casing of the integrated circuits on the carrier substrate is not required.
There is a technical problem to realize the advantages that reside in covering only the resonance element in an airtight casing to form a discrete component and applying this to the carrier substrate of the component module.
Considering the known systems described above, it should be regarded as a technical problem to create such circumstances on a component module so that a necessary SAW-component, necessary matching networks, such as inductance elements, integrated circuits, electric wiring and amplifiers (all of which earlier were coordinated in an evacuated airtight metal casing, physically separated and side-oriented from the component module pertaining to other functions) can be applied to the component module.
There is also a technical problem in being able to create the circumstances on the component module necessary to carry the complete oscillating circuit arrangement, achieving the requirements of a smaller spatial volume and a better coordination between utilized components then earlier known.
It is also a technical problem to create, on a component module, the circumstances necessary to allow the used resonance element (for instance, a SAW-component) and the two matching networks or elements (for instance inductances) to be oriented very close to each other and close to an integrated circuit, comprising among other things necessary amplifiers, and to in this manner create an embodiment that provides electromagnetic protection and electrical wiring with, for high frequencies, small parasitic capacitances.
There is also a technical problem in being able to realize the advantages in allowing the component module to include the functions necessary for a signal receiving circuit to be a part of the earlier mentioned integrated circuit, among other things.
Considering the known systems described above, it must also be seen as a qualified technical problem to be able to create the circumstances necessary to allow the complete oscillating circuit arrangement to be coordinated within a limited part of the surface of a module and to form on a surface area electrically conductive surface sections from the carrier substrate or circuit card belonging to the component module. These surface sections are formed and distributed in a way that they can coact with the corresponding contact surfaces of a resonance element, for instance a SAW-component, in a firm and electrically conductive manner. An integrated circuit, comprising the required signal amplifying circuit and further signal amplifying and/or signal processing circuits, is attached to the surface area adjacent to the surface sections and resonance element. The contact surfaces of the resonance element are connected to the contact surfaces of the carrier substrate by bonding or the like. The contact surfaces of the integrated circuit are connected to the contact surfaces of the carrier substrate by bonding or the like.
It is a technical problem to realize the advantages of adapting the component module to be a signal receiver and to allow the signal amplifying and/or signal processing circuit to be adapted to signal receiving and signal processing.
There is also a technical problem in realizing the advantages of forming further electrically conductive surface sections, from the carrier substrate or circuit card, on a surface area belonging to the component module, these further surface sections being formed and distributed in a way that they can coact with the corresponding contact surfaces of respective impedance elements in a firm and electrically conductive manner and being oriented adjacent to the surface areas belonging to the resonance element.
It is a further technical problem to be able to realize the advantages of orienting the necessary impedance elements adjacent to the resonance element, in the form of a SAW-element, and/or to the integrated circuit or to mount the integrated circuit, a SAW-component, and two impedance elements as discrete elements to the carrier substrate adjacent each other with the electrical wiring implemented on one surface of the carrier substrate so that the SAW-component, or the SAW-component with two impedance elements, is covered by an evacuated airtight casing.